This invention relates to a process for producing ortho- or paramonoalkylphenols or 2,4- or 2,6-dialkylphenols. More particularly, the invention relates to an alkylation process for phenols that have at least two replaceable hydrogens in the ortho- or para-position whereby the phenol is first converted to a t-alkylated phenol having at least one hydrogen in the ortho- or para-position. This t-alkylated phenol is reacted with an aldehyde and a secondary amine to form the aminoalkylated phenol that then is subjected to hydrogenolysis to produce an ortho- or para-alkylated, ortho- or para-t-alkylated phenol. The alkylated t-alkylated phenol is then contacted with an acid or acid reacting substance to give the alkylated phenol. Phenolic compounds with alkylated ortho-positions and/or para-positions are useful as various industrial materials. For example, 2,3,6-trimethylphenol is a desirable intermediate in the synthesis of vitamin E.
The method of t-alkylating phenols that have at least two open positions ortho-ortho or ortho-para to the hydroxyl group to form a t-alkylated phenolic compound still having at least one ortho- or para-position open is well known in the art. Thus contacting the phenol having at least two positions open with a branched olefin, a t-alkyl halide or a t-alcohol in the presence of an acidic catalyst is a common industrial practice. Such catalysts may be of the Bronsted type such as sulfuric acid, arylsulfonic acid, m-benzenedisulfonic acid, methanesulfonic acid, ion-exchange resin sulfonic acids or Lewis acids such as aluminum chloride, zinc chloride, magnesium chloride and the like. Alternately, phenoxides of certain metals such as aluminum, titanium, and zirconium have been used as taught by Ecke et al. (U.S. Pat. No. 2,821,898), Leston (U.S. Pat. Nos. 3,331,879; 3,267,153 and 3,267,155) and Hokama (U.S. Pat. No. 3,267,154). Still another way to introduce one or two t-alkyl groups into the nucleus of a phenolic ring is by the total t-alkylation of all the available ortho-para-positions followed by partial de-t-alkylation to obtain the desired partially t-alkylated phenol. Examples of this partial de-t-alkylation are given by Leston (U.S. Pat. Nos. 3,091,646 and 3,346,649), but de-t-alkylation may also be carried out by the convention process with Lewis or Bronstedt acids.
The method of alkylating phenols that have an open ortho- or para-position with an aldehyde and secondary amine to form aminoalkylated phenols that are then cleaved by hydrogenolysis to produce alkylated phenols is well known in the art. An example is U.S. Pat. No. 2,194,215 (Bruson et al.) which teaches the methylation of phenolic compounds by condensing the phenolic compounds with at least one molecular equivalent each of formaldehyde and a strongly basic, non-aromatic secondary amine to form phenolic tertiary amines. The phenolic tertiary amine obtained is then subjected to hydrogenolysis, whereby the secondary amine is reformed and a new methylated phenolic compound is produced. The hydrogenolysis is performed in the presence of the hydrogenation catalyst, copper chromite, at a temperature above 100.degree. C. and below 300.degree. C., and preferably between 150.degree. C. and 200.degree. C. By this process phenol can be converted into ortho-cresol, para-cresol, 2,4-xylenol, 2,6-xylenol or 2,4,6-trimethylphenol or mixtures thereof, depending upon whether one, two or three moles each of formaldehyde and a secondary amine are employed for the condensation.
Many hydrogenation catalysts are known in the art. These catalysts can exist in natural state or in the oxidized state. In referring to the oxidized state of a hydrogenation catalyst, the art generally refers to the oxidized hydrogenating components of the catalyst which are generally selected from the Group VIII metals of the Periodic Table of the elements and include iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and platinum. It is also known that these catalysts can be used as hydrogenolysis catalysts for cleaving compounds. An example of the use of some of these catalysts as hydrogenolysis catalysts is given in U.S. Pat. No. 3,946,086 (Gershanov et al.) which teaches a method for producing 2,6-dialkyl and 2,6-diaralkyl substituted derivatives of para-cresol. In this method phenol is alkylated with an olefin having from four to twelve carbon atoms or with styrene at a temperature in the range of 50.degree. C. to 150.degree. C. in the presence of a catalyst, namely, aluminum, to produce 2,6-dialkylphenol or 2,6-diaralkylphenol. The 2,6-dialkylphenol or 2,6-diaralkylphenol resulting from the alkylation is treated at with a mixture of formaldehyde and dimethylamine or with a reaction product thereof having the formula ##STR1## at a temperature of 20.degree. C. to 100.degree. C. to form N,N-dimethyl(3,5-dialkyl-4-hydroxybenzyl)amine or N,N-dimethyl(3,5-diaralkyl-4-hydroxbenzyl)amine. These tertiary amines are subsequently subjected to catalytic hydrogenolysis with either pure hydrogen or a hydrogen-containing gas, such as a methane-hydrogen mixture or a nitrogen-hydrogen mixture. The hydrogenolysis catalysts useful in this teaching are those that are conventionally used for this process, such as nickel, palladium, platinum, and copper. The teaching suggests that it proves more expedient to use a nickel-chromium catalyst, nickel-copper catalyst, and especially, alloyed nickel-aluminum-titanium catalyst. Also, the amination should be carried out in the medium of a saturated aliphatic alcohol such as monobasic aliphatic alcohols having one to four carbon atoms. The amination step must lead to the positioning of the alkyl groups in the para-position since the ortho-position is already occupied in the starting material. The products produced from the process of this teaching are the 2,6-dialkyl and 2,6-diaralkyl substitute derivates of para-cresol.
The final de-t-alkylation may be performed as described above with Bronstedt or Lewis acids or with metal phenoxides.
One skilled in the art is not taught by the aforementioned teaching as to how to produce phenols selectively alkylated in either the ortho- or para-position or di-ortho or di-ortho-para alkylated and having still one or two open ortho- or para-positions.
One skilled in the art is also not taught by the aforementioned teachings as to how to produce para-monoalkylated phenol or para-cresol in good yields and purity from a phenolic compound containing an open ortho- or para-position.